Quenching FITC

[m griep]

Michael, 
     I don't know how your samples are prepared but two possibil-
ities come to mind.  The first is to add anti-fluorescein 
(Molecular Probes sells some) to the mixture after the bacteria 
have been phagocytized.  Apparently, the binding of the anti-
fluorescein leads to quenching of the fluoresc.
     The second possibility is to lower the pH of the cell solution 
after the bacteria have been phagocytized.  The pK of fluorescein 
is typically 6.5 and the fluorescent species is the deprotonated
species.  So, lower pH to say 5.0 is enough to significantly 
reduce the fluorescence.

     Mark Griep
     mgriep at unlinfo.unl.edu


--
Mark Griep
Department of Chemistry      ____   ____      __________________
Center for Biotechnology    |    | /    |    |                  \_
University of Nebraska      |    |/     |    |                    \